Abu Sallam (may Allah have mercy on him) narrates from one of the Companions (may Allah be pleased with them) that he said: We raided a tribe of Juhaynah, and a Muslim man chased a man from among the disbelievers and struck at him with his sword; it missed him but struck himself. So he (peace and blessings be upon him) said: "Where is your brother, O Muslims!" The people searched and found that he had already been martyred. He (peace and blessings be upon him) led the funeral prayer for him in his clothes and with his blood, and buried him. The people asked: "Is he a martyr?" He (peace and blessings be upon him) said: "Yes, and I am a witness for him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16393